a) Field of the Invention
This invention relates to a balancer for a damper in a lockup clutch suitable for use in a torque converter.
b) Description of the Related Art
To facilitate the understanding of the present invention, reference is first had to FIGS. 16 and 17 of the accompanying drawings, in which FIG. 16 is a cross-sectional side view of an illustrative basic construction of a torque converter and FIG. 17 is an enlarged view of a damper section of the torque converter. In these drawings, there are shown a torque converter main body 10, an input shaft 1, a pump 2, a turbine 3, a stator 4, a turbine hub 5, a central axis 6, a power input casing 21, a clutch piston 22, retainer plates 23 fixed on the piston 22 by rivets 26, and tabs 24 each located on a radially inner side of a corresponding spring 32 which is in turn arranged on a radially inner side of an outer peripheral flange 28 of the piston 22. Each of these tabs 24 has been formed by radially slitting an outer peripheral portion of its corresponding retainer plate 23 at two locations apart from each other to divide the outer peripheral portion into a central part and side parts, with which the central part is flanked, and then bending the central part in a direction toward the turbine 3. Designated at numeral 25 are spring end face support members. Each of these spring end support members 25 has been formed by bending one of the side parts of the outer peripheral portion of the corresponding retainer plate 23 into a turned square U-shape with the open face of the U rendered broader and directed toward the turbine 3. There are also shown a friction member 27 of the clutch, a driven plate 31, and spacers 34 arranged on opposite sides of the spring 32.
Since the technology of torque converters is well known, its detailed description is omitted herein. It is however to be noted that, when an input shaft and an output shaft become equal in rpm, occurrence of a slip cannot be avoided between fluid couplings. To cope with this potential problem, a lockup clutch is arranged. When a hydraulic pressure is applied on a right side of the piston 22 as viewed in FIG. 16 and the piston 22 of the clutch is hence brought into contact under pressure with the input casing 21, the piston 22 and the input casing 21 are connected directly with each other. Resulting rotation of the piston 22 is transmitted to the driven plate 31 via the spring 32. Since the driven plate 31 is fixed on the turbine 3, the input casing 21 and an output shaft are directly connected with each other via a damper which includes the spring 32. This has made it possible to avoid any slip (FIG. 17 shows a double coil spring as an example of the spring 32 but, needless to say, the spring can be of any desired type).
A lock-up clutch equipped with such dampers must be kept balanced dynamically during rotation. However, no balancing hole can be formed through the piston because pressures are applied on both sides of the piston.
It was therefore proposed to form a balancing weight of such a folded clip type as shown in FIG. 13 and to bring it into fitting engagement with the retainer plate outwardly in a radial direction. Namely, this conventional clip-type weight designated at numeral 50 is formed of a front portion 51, an insert portion 52 as a back wall, and a folded portion 53. As is illustrated in FIG. 14, the clip-type weight 50 is mounted by inserting the insert portion 52 behind a back wall of the retainer plate 23. Designated at numeral 54 is a dowel which is brought into fitting engagement with a hole or recess in the retainer plate.
A balancer making use of the conventional weight of the folded clip type requires a substantial mounting space, and its insertion is difficult due to high spring force.